JP2002072797A - Apparatus and method for image formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can speedily stabilize the potential of a photosensitive body and immediately start forming an image. SOLUTION: This image forming apparatus which performs an image formation preparation stage for stabilizing the potential of the photosensitive body 1 at a specific potential prior to the start of image formation performs light irradiation by an image exposing means 9 in one starting round after the photosensitive body 1 begins to rotate in addition to light irradiation by a main electrostatic discharging light source 8, thereby immediately stabilizing the potential of the photosensitive body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electrophotographic image forming apparatus and an image forming method suitably applicable to such an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a transferable image is formed and carried on a first image carrier by an appropriate image forming process, and the transferable image is formed on a second image carrier.
In general, an apparatus having a system and a structure in which the image is transferred onto the image carrier and the first image carrier is repeatedly used for image formation is used.

For example, a general configuration of an image forming apparatus such as a copying machine or a laser beam printer of this type is as follows.
A rotating photoconductor such as a rotating drum as a first image carrier;
Charging means for uniformly charging the surface of the rotating photoreceptor to a predetermined polarity / potential; image exposing means for forming an electrostatic latent image on the charged surface of the rotating photoreceptor; Developing means for developing the image as an image, transfer means for transferring the toner image from the surface of the rotating photoreceptor to transfer paper as a second image carrier (recording medium), and a permanent fixed image of the toner image transferred to the transfer paper side And a photoreceptor cleaning unit (cleaner) for removing transfer residual toner remaining on the surface of the rotating photoreceptor without being transferred onto the transfer paper and cleaning the surface of the rotating photoreceptor.

The transfer paper subjected to the image fixing process by the fixing means is discharged as an image formed product (copy, print). The photoreceptor surface cleaned by the cleaning means is repeatedly used for image formation.

[0005] Selenium-based photoconductors, amorphous silicon (hereinafter a-Si) photoconductors, organic photoconductors and the like have been put into practical use as photoconductors used in conventional electrophotographic or electrostatic recording type image forming apparatuses. However, among them, it is known that the a-Si photosensitive member is particularly excellent in stability and durability.

Although the surface of the a-Si photoreceptor has a high hardness, the surface of the photoreceptor is sensitive to humidity and easily adsorbs moisture due to the influence of corona products generated by ozone generated from the charging means. It has the drawback of causing lateral flow of charges on the surface of the photoreceptor and deteriorating image quality, which is called image flow.

In order to prevent such image deletion, a method of heating with a heater as described in Japanese Utility Model Publication No. 1-305205, and a magnet roller and a magnetic toner as described in Japanese Patent Publication No. 2-38956 are used. A method for removing corona products by rubbing the surface of a photoreceptor with a brush formed from a brush, and a method for removing corona products by rubbing the surface of a photoreceptor with an elastic roller as described in JP-A-61-100780 Etc. are used.

On the other hand, as a charging method of the charging means, a contact charging method has been put into practical use instead of a corona charging method. In this method, a conductive contact charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type is brought into contact with a photoreceptor to be charged, and a predetermined charging bias is applied to the contact charging member. Is applied to charge the photoreceptor surface to a predetermined polarity and potential.A contact charger employing this type of method has a lower ozone and a lower ozone than a corona charger.
There are advantages such as low power.

The charging mechanism (charging mechanism, charging principle) of the contact charging system includes two types, a corona charging system and a contact injection charging system.
Types are mixed, and each characteristic appears depending on which is dominant.

The corona charging system uses a discharge phenomenon such as corona discharge generated in a minute gap between the contact charging member and the member to be charged, and charges the member to be charged with the discharge product. This corona charging system generates a very small amount of ozone, though much less than the corona charger.

The contact injection charging system is a system in which the surface of a member to be charged is charged by directly injecting charge from the contact charging member to the member to be charged. It is also called direct charging or injection charging.

Japanese Patent Application Laid-Open No. 6-3921 and the like disclose a charging roller, a fur brush, and conductive magnetic particles on a charge holding member such as conductive levels of a trap level or a charge injection layer on the surface of a photoreceptor. A method has been proposed in which charge is injected by a contact charging member such as a constrained magnetic brush to perform contact injection charging.

Since contact injection charging does not use a discharge phenomenon,
Only the portion where the member to be charged contacts the contact charging member is charged. For this reason, in order to perform good charging without uneven charging, the contact charging member and the member to be charged may have a peripheral speed difference, or the moving directions may be different from each other, and the contact probability between the member to be charged and the member to be contacted may be different. Should be high enough.

The contact injection charging does not have a threshold voltage for starting charging, the voltage required for charging is only the desired photoconductor surface potential, and is a low power and ozoneless charging system.

As a member to be charged which can be charged by contact injection, for example, in the case of an organic photoreceptor, it is necessary to provide a charge injection layer in which conductive fine particles are dispersed as a charge holding member on the surface of the photosensitive layer. In the case of an inorganic photoreceptor such as an a-Si photoreceptor, many trap levels based on crystal defects are present on the surface without newly providing a charge injection layer, and injected charges are held at the trap levels. Injection charging becomes possible.

Since contact discharge charging does not generate any discharge products, when the a-Si photosensitive member is combined with the contact injection charge, the image deletion which is a disadvantage of the a-Si photosensitive member can be fundamentally solved. There are advantages. Therefore, a
It is not necessary to constantly heat the Si photoreceptor with a heater or to provide a means for rubbing the photoreceptor surface with magnetic particles or an elastic member, so that power consumption can be saved and the apparatus can be simplified.

As a characteristic of the a-Si photosensitive member, when the light irradiation area and the dark area are simultaneously charged, the potential of the light irradiation area is extremely large in the dark area (dark decay), and the optical memory (afterimage phenomenon). Is liable to occur.

That is, the a-Si-based photoreceptor has many tangling bonds (unbonded bonds), which become localized levels to capture a part of the photocarriers and reduce its traveling property. Or reduce the probability of recombination of optical carriers. Therefore, in the image forming step, a part of the photocarrier generated by the exposure is a-
When an electric field is applied to the Si photoreceptor, the localized level is released at the same time as the electric field is applied, and a difference occurs in the surface potential of the a-Si type photoreceptor between the exposed portion and the non-exposed portion. Appears as.

Therefore, after the toner image is transferred onto the transfer paper, the photoreceptor is uniformly exposed to light by a light-elimination light source so that the number of photocarriers latent in the a-Si photoreceptor is increased so that the entire surface becomes uniform. Generally, erasing an optical memory is performed. At this time, the light amount of the neutralizing light emitted from the neutralizing light source is increased, or the wavelength of the neutralizing light is set to a
-The spectral sensitivity peak of the Si photoreceptor (about 600 to 700 n
By approaching m), it is possible to erase the optical memory more effectively.

Further, a-Si cannot be neglected due to dark decay due to heat-generated carriers, and the potential tends to fluctuate depending on the temperature. For this reason, in addition to the temperature control of the photoreceptor, the use of a potential stabilization method as described below prevents image deterioration due to environmental fluctuations.

That is, the potential of the photoreceptor latent image is measured by a potential sensor, the density of an image obtained by developing the electrostatic latent image is detected, and the detection signal is fed back to the charging means and the image exposure means in the image forming step. For example, US Pat. No. 2,956,487 describes a method for stabilizing an electrophotographic image by controlling a desired potential. Such an image stabilizing means is generally performed when the power of the apparatus is turned on, at the start of the image forming process, or at the end thereof.

[0022]

However, in the case of the above-described prior art, the following problems have occurred.

In the case of a photoconductor having a large number of localized levels acting as an electron trap, such as an a-Si photoconductor, after the start of image formation, the accumulation of photocarriers due to static elimination light proceeds, so that the potential of the photoconductor decreases. Phenomenon occurs.

As the charging step is repeated, the trapped photocarriers enter a steady state, and the potential stabilizes. The state in which the potential is stabilized means that the balance between the generation and accumulation of photocarriers due to static elimination light and the disappearance of photocarriers due to the release of trapped photocarriers due to recombination or charging of photocarriers is in a steady state, Light intensity of static elimination light,
It depends on the wavelength or charging voltage.

Therefore, when the power is turned on or before the start of the image forming process, the photoreceptor is uniformly exposed to static elimination light to bring the photocarrier of the photoreceptor into a steady state, and the charging voltage of the charging means is controlled to an optimum value. In general, an image forming preparation step for stabilizing the photoconductor potential is performed.

However, the potential control process cannot be started while the potential of the photoreceptor is lowered due to the exposure of the charge erasing light. This increases the length of time before the formation process is started.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to quickly stabilize the potential of a photoreceptor and to start an image forming operation in which image formation can be started immediately. An object of the present invention is to provide a forming apparatus and an image forming method.

[0028]

According to the present invention, there is provided an image bearing member, a charging means for charging the image bearing member to a predetermined potential, and irradiating the image bearing member with light. And an exposure unit for forming an image. The image forming apparatus further includes: a potential stabilizing unit that stabilizes a potential of the image carrier prior to the start of an image forming step, wherein the potential stabilizing unit includes the exposing unit. It is characterized by including.

In addition, it is preferable that the image bearing member has a neutralizing light irradiating means for uniformly exposing the image carrier to erase an optical memory, and the potential stabilizing means includes the neutralizing light irradiating means.

The image bearing member is provided endlessly,
The exposure unit may expose at least one round of the image carrier when stabilizing the potential of the image carrier.

Further, it is preferable that the surface layer of the image carrier has amorphous silicon.

The charging means may include a conductive charging member, and the charging member may be brought into contact with the image carrier to charge the image carrier.

Further, the charging means may be a corona charger.

In the image forming method of the present invention,
A first method of forming an image on an image carrier by irradiating light from exposure means
And a second exposure step for uniformly exposing the image carrier by the exposing means to stabilize the potential of the image carrier.

The second exposure step is preferably a step performed prior to the start of the image forming step.

The second exposure step is preferably a step performed over at least one rotation cycle of the image carrier.

[0037]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

(First Embodiment) An image forming apparatus according to a first embodiment will be described with reference to FIGS.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment, FIG. 2 is a view illustrating an image forming method of the image forming apparatus according to the present embodiment, and FIG. FIG. 4 is a graph showing a change in potential, and FIG. 4 is a schematic diagram of a cross section of a photoconductor of the image forming apparatus according to the present embodiment.

First, the configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG.

In the figure, reference numeral 1 denotes a cylindrical a-Si photosensitive member (image carrier) which rotates at 150 mm / sec in the direction of the arrow in the figure. 2 is a magnetic brush charger (charging means) of a charge injection type using a magnetic brush, 9 is an image exposure means (exposure means) for generating a laser beam having a central emission wavelength of 680 nm, 3 is an image exposure means on the photoreceptor 1 A developing device for forming a toner image corresponding to the electrostatic latent image formed by irradiating the laser light L from 9;
Is a transfer roller that electrostatically transfers the toner image formed on the photoconductor 1 to the transfer material P, 5 is a cleaner that collects the transfer residual toner remaining on the photoconductor 1 after the transfer process, and 6 is the transfer material P
A fixing unit 7 for thermally fixing the upper toner, a potential sensor 7 for detecting a potential on the photoconductor 1, and 8 a photoconductor 1 after transfer
This is a main charge removing light source (discharge light irradiating means) for erasing the potential remaining in the device.

S1 is a power supply for applying a charging voltage to the magnetic brush charger 2, S2 is a power supply for applying a developing bias, 10
Is a control device that changes the output values of S1 and S2 based on the measurement value of the potential sensor 7.

In the above configuration, charging, exposure, development, and development are performed based on a well-known electrophotographic process.
Image formation is performed continuously by repeating the steps of transfer, fixing, and cleaning.

Hereinafter, the configuration of each part of the image forming apparatus according to the present embodiment will be described in more detail.

The image exposure means 9 includes a laser element (not shown),
This is a known laser optical system including a collimator lens system, a polygon mirror, and an Fθ lens system. The laser element is a semiconductor laser having a central emission wavelength of 680 nm and an output of 2 μJ / cm ^2.
M drive.

The developing device 3 used in the present embodiment has a rotatable sleeve 15 enclosing a fixed magnet roll 14. The developer in the developing container 17 is thinned by a blade 18. The layer is coated on the sleeve 15 and transported to the developing section. The distance between the nip between the sleeve 15 and the photosensitive member 1 is 500 μm, and the amount of developer carried on the sleeve 15 is set to 40 mg / cm ² . At this time, the sleeve 15 is rotating at a peripheral speed of 150 mm / sec in the direction of the arrow.

The developer used in the present embodiment is a two-component developer, having a negatively chargeable toner of 8 μm and a positively chargeable toner of 50 μm.
μm magnetic carrier at a toner concentration of 5% by weight. The toner density is controlled by an optical toner density sensor (not shown), and the toner in the toner hopper 20 is supplied by the supply roller 23. The developer in the developing container 17 is uniformly stirred by the stirring members 21 and 22.

The sleeve 15 has a voltage of 2 kVp from the power source S2.
A developing bias in which a variable DC voltage Vdc is superimposed on an alternating electric field of p, 2 kHz is applied. The developer coated in a thin layer and conveyed to the developing unit contributes to the development of the electrostatic latent image on the photoconductor 1 by the electric field by the AC + DC voltage.

The magnetic brush charger 2 includes a rotatable sleeve 31 and a magnet roller 3 fixed in the sleeve 31.
0, a voltage obtained by superimposing an alternating electric field of 400 Vpp and 1 kHz on a variable DC voltage Vc from a power supply S1 is applied to the sleeve 31 during image formation. The application of an alternating electric field as a charging bias is effective in improving the charging ability and preventing a positive ghost.

The magnetic particles are held on the sleeve 31 by the magnetic restraining force of the magnet roller 30, and the thickness of the magnetic particle is regulated by the blade 32 having an interval of 700 μm between the sleeve 31 and the photosensitive particle 1. Do.

The sleeve 31 is 200 mm / s in the direction of the arrow.
It rotates at a peripheral speed of ec. The amount of magnetic particles carried on the sleeve 31 when the photosensitive member 1 is not in contact with the photosensitive member 1 is 170 mg / cm ^2.
Met. The gap between the photoconductor 1 and the sleeve 31 in the nip is 500 μm, and the magnetic flux density by the magnet on the sleeve 31 of the charging unit is 800 × 10 ⁻⁴ T. As the magnetic particles of the magnetic brush, the average particle size is 25 μm, the resistance value is 5 × 10 ⁶ Ω · cm (5 × 10 ⁴ Ωm), and the saturation magnetization is 2 μm.
The one having a value of 00 emu / cm ³ (about 0.251 Wb / m ² ) was used.

The magnetic brush injection charging is a charging method in which conductive magnetic particles are brought into contact with a member to be charged, and charges are directly injected. Compared with corona charging or roller charging using a discharge phenomenon, the injection charging system has no advantage in that no discharge occurs, and thus has the advantage that the resistance change of the photoconductor surface due to the discharge product does not occur.

The surface resistance of the a-Si photoreceptor tends to fluctuate particularly due to discharge products, and in a high-humidity environment, blur or flow of the electrostatic latent image due to a decrease in the surface resistance tends to occur. For this reason, it is necessary to provide a heater in the cylinder of the photoreceptor and to suppress this phenomenon by heating. When the injection charging method is used for such a photoreceptor, the dependence on the heater can be reduced because there is no influence by a discharge product.

In the case of using the injection charging method, it is necessary to provide a charge injection site by dispersing conductive particles such as tin oxide in the surface layer of a photosensitive member using an organic semiconductor. Has sufficient charge injection sites on the surface without giving any special prescription, and has very excellent charging characteristics.

Therefore, in this embodiment, an a-Si photosensitive member is used as the photosensitive member 1. FIG. 4 shows a schematic diagram of a cross section of the photoconductor used in the present embodiment.

The photosensitive member 1 used in this embodiment has a diameter of φ60.
And a charge injection blocking layer, a photoconductive layer and a surface layer sequentially laminated on the surface of the conductive support. Here, the charge injection blocking layer is for preventing charge injection from the conductive support into the photoconductive layer, and the photoconductive layer is made of an amorphous material containing silicon atoms as a main raw material. Is shown. Further, the surface layer contains silicon atoms and carbon atoms, and is responsible for holding an electron latent image formed on the surface and improving the durability of the film.

The a-Si photosensitive member has a very high surface hardness,
It shows high sensitivity to long wavelengths such as semiconductor lasers, and hardly shows any deterioration due to repeated use, so that it is suitable as a photoconductor for electrophotography.

The a-Si photoreceptor has a large dark decay, and it is desirable to minimize the amount of static elimination light in order to efficiently obtain a required potential. On the other hand, the optical memory using the residual optical carrier due to the image exposure tends to be improved as the amount of the charge removing light increases, so that the light amount of the main charge removing light source 8 may be set to the minimum light amount at which the optical memory is at an allowable level. The wavelength of the main charge removing light source 8 is desirably a light source having a light emission center wavelength appropriately shorter than the spectral sensitivity peak of the photoconductor 1. In the present embodiment, the emission center wavelength is 660 n
m of the LED as the main static elimination light source 8 and 150 mm / s
The photosensitive member 1 rotating at ec was set to emit light at 10 lx · s.

The cleaner 5 includes a cleaning blade 33
And a screw 34 for transporting the toner removed from the photosensitive member 1 to a waste toner container (not shown).
Consists of

In the above configuration, when the image forming process is started, the photosensitive member 1 is uniformly charged to a predetermined potential by the magnetic brush charger 2, and then the laser beam corresponding to the image is L is irradiated (first exposure step), and an electrostatic latent image is formed on the surface. The electrostatic latent image is visualized as a toner image by a developing device 3 carrying charged toner particles, and the toner image is electrostatically transferred to a transfer material P by a transfer roller 4 to form an image formed product.

After the transfer of the toner image, the main charge removing light source 8
After the photoreceptor 1 is uniformly exposed to light and the optical memory on the photoreceptor 1 is erased, the transfer residual toner remaining on the photoreceptor 1 is collected by the cleaner 5. The photoreceptor 1 cleaned by the cleaner 5 repeats the above operation,
Continuously used for image formation.

In order to form a stable and high-quality image in the image forming step, the charging applied to the magnetic brush charger 2 based on the photoconductor potential measured by the potential sensor 7 prior to the start of the image forming step. An image forming preparation step of controlling voltage and the like is executed. In the present embodiment, initial potential control for setting a charging potential and a developing potential is performed when the power of the apparatus is turned on, and a potential fluctuation due to a change in the temperature in the apparatus during standby is corrected before the image forming process is started. Potential correction is performed.

A method of controlling the initial potential will be described. The charging voltage is set to predetermined voltage values Vh and Vl, and two types of image exposures L ₀₀ and L _FF are performed at each charging voltage, thereby measuring four types of photosensitive member potentials. Photoreceptor potential relative L ₀₀ exposure for charge voltage Vh and the charging voltage Vl
L ₀₀ obtains the L ₀₀ curves from the photosensitive member potential to the exposure time, obtaining the L _FF curve from the photosensitive member potential to the L _FF exposed in the same manner. L ₀₀ the curve obtained by subtracting a predetermined constant from the curve L
_The charging voltage value and the developing DC voltage value are calculated from the difference between the L _cont curve and the L _FF curve so that an appropriate contrast potential V _FF −V _cont is obtained.

In the potential correction, the photoconductor potential at the time of the initial potential control is compared with the photoconductor potential at the time of receiving the image formation start command, and the charging voltage is corrected based on the difference.

Next, an image forming method of the image forming apparatus according to the present embodiment will be described with reference to FIG. In the figure, the hatched portions indicate that the motor, the ramp, the bias, and the like are operating.

When the power switch of the apparatus is turned on, heating of the fixing device 6 is started, and at the same time, an image forming preparation step at the time of power-on is executed. As shown, the drum motor and the developing motor are driven to drive the photosensitive member 1 and the developing device 3.
Is turned on, and the charging bias and the main charge removing light source 8 are turned on.

Immediately after the start of the image forming preparation process, while the photoreceptor 1 makes one rotation (one rotation), the image exposing means 9 is also illuminated in addition to the main discharging light source 8 as potential stabilizing means (second).
Exposure step). The image exposure means 9 is continuously lit (full lit) so that the maximum amount of light is obtained during one rotation of the photoconductor 1. Then, after the photoconductor 1 makes one round, the full lighting of the image exposure means 9 is released, and the above-described initial potential control is started.

The laser light of the image exposing means 9 has a wavelength closer to the spectral sensitivity peak of the photosensitive member 1 than the static elimination light of the main static elimination light source 8, and is exposed with a very large amount of light when fully lit. Therefore, the light carrier can be saturated only by exposing one round of the photoconductor 1. Therefore, the surface potential of the photoreceptor 1 can be immediately stabilized, and high-precision potential control can be quickly performed.

When the initial potential control is completed, the main discharge light source 8, the image exposure means 9, and the charging bias are turned off. Further, when the fixing device 6 reaches a predetermined temperature, the drum motor and the developing motor are also turned off, and the image forming apparatus enters a standby state.

When an image formation start instruction is received,
An image forming preparation step is performed before the image forming step. As in the image forming preparation process at the time of turning on the power, the image exposure unit 9 is fully turned on in addition to the main static elimination light source 8 for the first round of the photoconductor 1, and the surface potential of the photoconductor 1 is stabilized. Potential correction is performed. The image forming process is started in a state where the photoconductor potential and the development contrast are controlled appropriately.

Next, the potential control step of the image forming apparatus according to the present embodiment will be described in more detail with reference to FIG.

FIG. 3 is a graph schematically showing the change in the surface potential of the photosensitive member.
That is, the drum motor, static elimination light source, and charging bias are turned on.
The vertical axis indicates the surface potential of the photoconductor 1 detected by the potential sensor 7. A graph (a) indicated by a solid line indicates a change in surface potential in the image forming apparatus according to the present embodiment, and a graph (b) indicated by a dotted line indicates an image forming apparatus according to the related art (light irradiation only by the main static elimination light source 8). Of the surface potential change in the prior art).

In order to perform high-precision potential control in a potential control step such as initial potential control or potential correction, first, the surface potential of the photosensitive member must be in a stable state.
However, in the case of a photoconductor such as an a-Si photoconductor, which contains many electron traps in the photoconductive layer, photocarriers gradually accumulate by light irradiation of only the main static elimination light source 8, so that the dotted line (b) in FIG. Shows the initial charging characteristics shown in FIG.

In the conventional example (b), it can be seen that it takes about 15 to 20 seconds after the charging bias is turned on until the photosensitive member potential is stabilized. After receiving the image formation command,
It is preferable that the image be output earlier,
When a photoconductor such as a-Si is used, it is not possible to immediately proceed to the potential control step for such a reason, and the first copy time becomes long.

Therefore, as described above, in the present embodiment, in response to the image forming command, the photosensitive member 1 starts rotating and the first round of rotation, in addition to the main discharging light source 8 as the potential stabilizing means, the image exposing means 9 by irradiating light,
Immediately stabilizes the potential of the photoconductor.

The graph showing the change in the photoconductor surface potential in this case is shown by the solid line (a) in FIG. 3, and it can be seen that unlike FIG. 3 (b), the photoconductor surface potential is immediately stabilized. Therefore, it is possible to immediately proceed to the potential control step after the photoconductor 1 makes one round.

The rotation speed of the photosensitive member 1 is detected by a photosensitive member position detecting means (not shown). At this time, the photoconductor 1
It is necessary to control the timing of turning on the main static elimination light source 8 and the image exposure means 9 so that the same amount of light is irradiated uniformly over the entire surface of the device.

It should be noted that if the amount of light applied to the photoreceptor 1 is not uniform, ripples in the surface potential of the photoreceptor will be caused, making it impossible to control the potential accurately.

In the potential control of the present embodiment, the developing contrast potential V _FF -V _cont is set to be controlled to 200 V, and Vc at that time is approximately 750 V, Vdc.
Is about 250V.

Note that the image forming preparation step and the potential control step described in the present embodiment are merely examples, and for example, a-Si
Depending on the characteristics of the photoreceptor and the rotation speed of the photoreceptor, the appropriate light emission amount and wavelength of the main static elimination light source 8 or the image exposure means 9 are not limited to those described in the present embodiment.

In the image forming preparation step, the same effect can be obtained by causing the image exposure means 9 to emit light not only for one rotation of the photosensitive member but also for two or more rotations.

As described above, in the image forming apparatus of the present embodiment, in the image forming preparation step, the image exposing means 9 is caused to emit light together with the main charge removing light source 8 before the potential control is started. As a result, the body surface potential can be quickly stabilized and the potential can be controlled immediately, and the first copy time can be reduced.

(Second Embodiment) FIG. 5 shows a second embodiment. In the first embodiment,
Although the magnetic brush charger is used as the charging unit, the present embodiment is characterized in that a conductive fur brush is used.

Since other structures and operations are the same as those of the first embodiment, the same components are denoted by the same reference numerals and description thereof will be omitted.

The fur brush 40 used in this embodiment has a core bar having an outer diameter of 7 mm, a bristle length of 3 mm, and a flocking density of 100,000 / inch ² (about 15,500 / c).
m ² ), a cylindrical material having a total outer diameter of 13 mm in which conductive fibers having a resistance value of 1 × 10 ⁶ Ω were planted.

The nip width with the photosensitive member 1 is about 3 mm.
The rotation direction is the counter direction with respect to the photoconductor 1, and the rotation speed is 150 mm / sec.
0 rotates at 150 mm / sec. A voltage is applied to the fur brush 40 from the power supply S3, and the voltage is variable by the control device 10.

The fur brush 40 can also perform injection charging by optimizing its electric resistance. There is a disadvantage that the contact density is small and the charging uniformity is inferior to that of the magnetic brush injection charging, but it is used because the device configuration is simple.

Also in the present embodiment, in the image forming preparation step, the image exposure means 9 is made to emit light together with the main charge elimination light source 8 before the potential control is started, so that the surface potential of the photosensitive member is quickly stabilized and the potential control is immediately performed. The first copy time can be shortened.

(Third Embodiment) FIG. 6 shows a third embodiment. In the first embodiment,
Although the magnetic brush charger is used as the charging means, the present embodiment is characterized in that a corona charger is used. A heater for heating the photoconductor and a control device for controlling the temperature of the photoconductor are provided in the photoconductor 1 (not shown).

The other configuration and operation are the same as those of the first embodiment, so that the same components are denoted by the same reference characters and description thereof is omitted.

The discharge wire 45 has a voltage of -10 from the power source S4.
A charging bias by a constant current control of 00 μA is applied. The grid 46 is a power source S5 that can control the applied bias.
The grid application bias is changed during initial potential control and potential correction.

The corona charging method has disadvantages such as the necessity of heating the photoreceptor 1 under the influence of a discharge product such as ozone. However, the corona charging method is widely used because of its simple structure and high durability. I have.

Also in the charging method in which charge is applied to the photosensitive member 1 in a non-contact manner as in the present embodiment, the image exposing means 9 is made to emit light together with the main discharging light source 8 before the potential control is performed in the image forming preparation step. As a result, it becomes possible to stabilize the surface potential of the photoreceptor quickly and immediately control the potential,
The first copy time was shortened.

[0094]

As described above, according to the present invention,
Since the image carrier is exposed by the exposure unit during the image forming preparation process, more photocarriers are generated and accumulated on the image carrier, and the potential of the image carrier can be stabilized quickly, and the potential control of the charging unit is immediately performed. Can be performed, and the first copy time can be shortened.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an image forming method of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a graph showing a change in photoconductor surface potential.

FIG. 4 is a schematic sectional view of a photoconductor of the image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of an image forming apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 2 magnetic brush charger 3 developing device 4 transfer roller 5 cleaner 6 fixing device 7 potential sensor 8 main static elimination light source 9 image exposure means 10 controller 30 magnet roller 31 sleeve 32 blade 40 fur brush 45 discharge wire 46 grid S1 , S2, S3, S4, S5 power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/04 F term (Reference) 2H003 AA01 BB11 BB14 CC01 CC04 CC06 DD03 2H027 DA02 DE05 DE07 EA02 EA10 EC06 EC15 ED15 2H035 AA09 AA10 AC02 AC03 AC06 2H068 DA03 DA05 FA12 2H076 DA06 DA09 DA17

Claims (9)

[Claims] An image forming apparatus comprising: an image carrier; charging means for charging the image carrier to a predetermined potential; and exposure means for irradiating the image carrier with light to form an image. An image forming apparatus comprising: potential stabilizing means for stabilizing the potential of the image carrier prior to the start of the forming step, wherein the potential stabilizing means includes the exposure means. 2. The apparatus according to claim 1, further comprising: charge erasing light irradiating means for uniformly exposing said image bearing member to erase an optical memory; and said potential stabilizing means includes said charge erasing light irradiating means.
An image forming apparatus according to claim 1. 3. The image carrier according to claim 1, wherein the image carrier is provided endlessly, and the exposure unit exposes at least one round of the image carrier when stabilizing the potential of the image carrier. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein a surface layer of said image carrier has amorphous silicon. 5. The charging means has a conductive charging member,
The image forming apparatus according to any one of claims 1 to 4, wherein the charging member is brought into contact with the image carrier to charge the image carrier. 6. An image forming apparatus according to claim 1, wherein said charging means is a corona charger. 7. A first exposure step of irradiating light from an exposure unit to form an image on an image carrier, and uniformly exposing the image carrier by the exposure unit to stabilize the potential of the image carrier. And a second exposure step. 8. The image forming method according to claim 7, wherein the second exposure step is a step performed before the start of the image forming step. 9. The image forming method according to claim 7, wherein the second exposure step is a step performed over at least one rotation cycle of the image carrier.